![]() ![]() The lack of single crystals and strongly overlapping broadened reflections in powder diffraction patterns impeded further characterisation. The latter’s metrics and approximate composition as determined by TEM methods revealed the presence of a new sulfide telluride. The copper crossbar functions as a “landmark” a side-phase visible in the centre of the scan contains no Te, whereas the crystals on the right side of the scans are located too close to the copper bar to be measured independently.Īs an example, the very unusual compound Pb 8Sb 8S 15Te 5 was found in quenched samples with the nominal composition “Pb 5Sb 4S 6Te 5” that contained a mixture of PbTe, Sb 2Te, and an unknown quaternary phase. 28: TEM image of the selected crystallite on a copper grid (left, scanned region marked by black box) and an enlarged image of the measured tip of the crystallite (0.3 × 0.5 × 1 μm 3) with centre of rotation (top right), and a schematic representation of fluorescence line scans of Cu, Te and S (bottom right). Crystallites were pre-characterised by TEM and re-located at the beamline by fluorescence scans so that diffraction data could be acquired.įig. TEM and microdiffraction were efficiently combined by using microcrystalline samples on carbon-coated copper grids. Transmission electron microscopy (TEM), on the other hand, is a reliable tool for the discovery of such new phases and the determination of their unit-cell metrics by electron diffraction and their chemical composition by energy-dispersive X-ray spectroscopy. However, it would be extremely tedious to identify a good crystallite of a new compound that occurs as a side phase in heterogeneous materials. This enables precise X-ray structure analyses of microcrystals which can be centred by detecting their characteristic X-ray emission while moving the sample in the beam (fluorescence scans, Figure 28). The very stable beam at beamline ID11 can be focused to diameters of less than one micrometre by refractive lenses. Despite recent advances to overcome the problem of dynamical diffraction, electron crystallography still cannot compete with the accuracy of single-crystal structure analyses. Powder X-ray diffraction is, in many cases, insufficient for the precise and accurate characterisation of such materials with unknown structure types. Structure analyses of compounds present in heterogeneous samples can be demanding, especially if metastable phases or the products of precursor reactions do not exhibit crystals with sizes required for conventional structure analysis. ![]()
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